A biochemical and physiological study of nicotine sensitive cells is conducted to explore the biological basis of behavior of compulsive smoking. The hypothesis that nicotinic cholinergic receptors on nerve cells change in number and function with chronic exposure to nicotine is examined utilizing a neuron-like cultured cell line, rat brain tissue, and avian retina tissue. Tritium labeled bromoacetylcholine is developed as a probe to measure nicotinic receptors on nerve cells and to test the effects of chronic nicotine exposure.